Vehicles in which the cab tilts up to provide access to the vehicle's engine are generally referred to as “tilt-cab” vehicles. The cab, the enclosed space where the driver is seated, in a tilt-cab vehicle is typically positioned over the engine and front axle. As a result of this stacked design, tilt-cab vehicles are generally shorter than an equivalent conventional cab vehicle, where the cab is positioned behind the engine and front axle.
The cab in a tilt-cab design generally has two positions. In the driving position, the cab body is engaged and resiliently supported on the vehicle chassis and orientated such that the vehicle can be driven. In the maintenance position, the cab is tilted upward at a pivot point near the front of the cab to provide access to the engine and other mechanisms.
For tilting a resiliently mounted cab, it is known to use a hydraulic tilting device disposed between the chassis and the tilting cab to raise and lower the cab between the driving and maintenance positions. In order to ensure that the tilting device does not interfere with the spring movements of the cab relative to the chassis while the vehicle is being driven, tilting devices with a so-called lost motion capability are used. These tilting devices can be divided largely into mechanical types and hydraulic types. Mechanical types have, for example, a lost-motion arm, which is usually pivotably connected between the tilting cylinder and the cab, or a sort of pin-and-groove connection between the tilting cylinder and the cab. The lost motion capability is provided by the mechanical play in the pin-and-groove connection.
Hydraulic types have, for example, a dual acting hydraulic actuator to provide the lost motion effect. Dual acting hydraulic actuators contain two internal hydraulic cavities. Supplying hydraulic fluid to the push cavity will cause the actuator to extend in length, thereby exerting force to tilt the cab upward. Supplying hydraulic fluid to the pull cavity will cause the actuator to contract in length, thereby exerting force to lower the cab downward. To provide lost motion capability, it is known to place the push cavity in fluid communication with the pull cavity. As the resiliently mounted cab bounces on the chassis and pushing and pulling forces are exerted on the actuator, the motion of the hydraulic fluid between the push and pull cavities allows the actuator to extend and contract with relative ease, providing lost motion.
While a dual acting hydraulic actuator offers a means of providing lost motion in a tilt-cab design, a dual acting hydraulic actuator is not always necessary to fulfill the cab tilt functionality. A single acting actuator is sufficient to provide a means for cab tilt because gravity is sufficient to provide the downward force to lower the cab. In addition, dual acting actuators are generally more complex than single acting actuators. As a result, dual acting actuators are more costly and are less reliable than single acting actuators. Accordingly, it would be an advance in the state of the art to provide an alternative means of providing a hydraulic actuator with lost motion capabilities suitable for use in a tilt-cab design.